Subsea cables of this kind, or umbilicals as they are often called, are widely used in offshore oil and gas recovery. The subsea cable is designed to transport chemicals, hydraulic fluid, electric power and/or electrical control and pilot signals. In particular in those cases where the subsea cable is designed to extend from a floating structure, for example, a ship, on the sea surface down to a subsea structure on the sea floor, it is essential that the cable has a particular course, so that relative movements between the ship and the sea floor do not exert excessively large loads on the cable. To achieve this course it is known to hang weight elements onto parts of the cable whilst other parts of the cable are preferably equipped with floats.
U.S. Pat. No. 6,146,052 discloses a dynamic control cable string or umbilical which hangs in catenary form between a connection point on the seabed and a connection point located at the sea surface. In this case, the cable extends approximately vertically from the ship and then extends in a gentle curve a short distance upwards, in order subsequently in a gentle curve downwards again and finally into an approximately horizontal course at the sea floor.
According to this prior art document, gravity elements are placed on the umbilical with the main purpose of obtaining a submersible section. These gravity elements are only required when the umbilical's own weight is such that the umbilical tends to float or when the unloaden weight is not sufficient to make the umbilical hang in the desired catenary form.
The attached weight elements complicate the deployment operation, leading to increased cost. In addition, the weight elements project from the cable, thus risking to be stuck or be pulled off during the deployment operation. Finally, since the weight elements are designed to obtain a submersible section and not to provide an anchoring effect to the sea floor, the longitudinal stability is not optimal.
To eliminate or greatly reduce the need of attached weight elements it is disclosed in U.S. Pat. No. 6,046,404 that the weight element comprises at least one strength member which extends continuously along the entire length of the cable, to which strength member there is attached a weight element/weight elements.